As electronic devices become smaller, the requirements for precise electrical connection at extremely fine pitch continue to increase. As an example, semiconductors, such as integrated circuits, are formed on wafers that are then cut into dice or chips that individually may be mounted on substrates. Typically, the substrate has fine electrically conductive circuit lines, and electrical and thermal contact must be made between the substrate and chip. As electronic appliances, such as computers, tape players, televisions, telephones, and other appliances become smaller, thinner, and more portable, the size requirements for semiconductors and the means for providing electrical connection between semiconductors and substrates, or between flexible circuits and rigid printed circuits, become increasingly demanding.
One method for providing electrical conductivity between two electrical elements is through the use of a Z-axis conductive sheet material, such as a Z-axis adhesive. Whether the sheet material is an elastomer or an adhesive, the continuing challenge is to keep pace with the miniaturization in the electronics industry. Z-axis conductivity can be achieved through a number of means, including dispersing conductive particles throughout a binder matrix. Where electrical connection on a very fine pitch is required, the conductive elements may be placed only where the electrodes are located, typically requiring indexing the conductive sheet to the electrodes, or the conductive elements may be placed at such close spacing, relative to the spacing of the electrodes, that indexing is not required. U.S. Pat. No. 5,087,494, (Calhoun et al) is an example of an electrically conductive adhesive tape having conductive particles placed at precise locations, on a fine pitch. The Calhoun et al '494 patent also discusses a number of available options for electrically conductive adhesive tapes.
U.S. Pat. No. 4,008,300 (Ponn) and U.S. Pat. No. 3,680,037 (Nellis, et al.), teach a dielectric sheet material having a plurality of compressible resilient conductive plugs that extend between the faces of the sheet. The sheet can be placed between circuits to make electrical connection there between. The conductive plugs of Ponn and Nellis are dispersions of conductive particles in a binder material.
U.S. Pat. No. 5,522,962 teaches conductive sheets that are conductive through the thickness but insulating in the lateral directions. While conductive materials are disclosed, they tend to have low light transmission and therefore are not particularly useful in transmission devices such as liquid crystal displays. Further, the conductive materials utilized in the invention are conductive ferromagnetic particles coated in a binder.
Metallic reflectors are often used in optical displays, such as liquid crystal displays, to even out illumination across the display and to diffusely reflect the light from the backlight or light coming in the display from the environment. Prior art reflectors include planar specular reflectors and planar diffusive reflectors. Specular reflectors include a substantially planar surface that is covered with a reflective metallic coating. Specular reflectors are characterized by an angle of incidence being substantially equal to an angle of reflection. Diffusive reflectors typically have a roughened surface which is predominately coated with a metallic reflective coating. Diffusive reflectors are characterized by reflecting and scattering incident light. Prior art diffuse reflectors typically comprise continuous metallization of a roughened polymer sheet.
The transmission-type LCD includes a backlight, typically one to two cold fluorescent bulbs at the back surface of the liquid-crystal panel. The backlight consumes a relatively large amount of power. The diffuse reflector evens out the illumination of the back light across the entire display to eliminate any hot (brighter) spots. The more efficient a reflector is at diffusing, the more even the light will be across the display. The more efficient the reflector is, minimizing the amount of light lost to transmission and absorption, the more light passes through the liquid crystal and is realized as a brighter screen. This more efficient diffuse reflector can be used for a brighter display or for less power use that extends battery life
Reflection-type LCDs include a reflector for reflecting light at a back surface of the LCD, in which ambient light is reflected on the reflector to display images. The diffuse reflector reflects and diffuses the ambient light to mask any hot spots due to differences in ambient lighting across the display. The more efficient the reflection and diffusion of the reflector is, the brighter the display can be. This display does not use a backlight reducing the amount of required power but the ambient light reflection cannot produce satisfactory brightness for vivid color images and is used on calculator and other text displays.
U.S. Pat. No. 5,917,567 (Oh at al.) relates to a reflector having diffusion characteristics in which the surface of the reflector is formed with a plurality of convex portions by uniformly depositing fine spacers. The reflector is manufactured by providing a substrate, forming a thin layer of a solution of beads and polymer on the substrate, and forming a reflective layer on the thin layer. The beads form simple reflective lenses as compared to the complex lenses used in this invention. Complex lenses provide more efficient diffusion because of the multitude of lens surfaces and thus provide more efficient diffusion than can be obtained with a simple lens diffuse reflector.
It is known to produce polymeric film having a resin coated on one surface thereof with the resin having a surface texture. This kind of polymeric film is made by a thermoplastic embossing process in which raw (uncoated) polymeric film is coated with a molten resin, such as polyethylene. The polymeric film with the molten resin thereon is brought into contact with a chill roller having a surface pattern. Chilled water is pumped through the roller to extract heat from the resin, causing it to solidify and adhere to the polymeric film. During this process the surface texture on the chill roller's surface is embossed into the resin coated polymeric film. Thus, the surface pattern on the chill roller is critical to the surface produced in the resin on the coated polymeric film.
The U.S. Pat. No. 6,285,001 (Fleming et al) relates to an exposure process using excimer laser ablation of substrates to improve the uniformity of repeating microstructures on an ablated substrate or to create three-dimensional microstructures on an ablated substrate. This method is difficult to apply to create a master chill roll to manufacture complex random three-dimensional structures and is also cost prohibitive.
In U.S. Pat. No. 6,124,974 (Burger) the substrates are made with lithographic processes. This lithography process is repeated for successive photomasks to generate a three-dimensional relief structure corresponding to the desired lenslet. This procedure to form a master to create three-dimensional features into a plastic film is time consuming and cost prohibitive.
In U.S. Pat. No. 6,266,476 (Shie et al.) a monolithic element having a substrate body and a macro-optical characteristic produced by surface micro-structures. These micro-structures can be non-uniform across the lens to minimize certain lens aberrations. These non-uniform micro-structures reduce lens aberrations, but are not able to significantly alter the macro-optical characteristics of the optical body. The diffusing structures, in this invention, vary as to change the macro diffusion efficiency across the diffusion film. The diffusion elements can vary changing the diffusion characteristics of the diffusion area from diffusing most of the light to letting light pass specularly which micro-structures are unable to do.